The major urinary metabolite of the pineal hormone melatonin, 6-hydroxymelatonin is being quantified by gas chromatography-negative chemical ionization mass spectrometry. Urinary excretion rates of this metabolite are being used to determine the possible role of the pineal gland in the development of puberty in normal children or during normal menstrual cycles. Longitudinal studies on prepubertal girls are in progress. A study on seasonal variations in pineal function is in progress. The use of pineal hormone metabolites as an index of noradrenergic function in various clinical states is being pursued.